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First Law of Thermodynamics

• Two objects are in thermal equilibrium if they do not exchange heat when in contact.
• Zeroth law of thermodynamics: If A and B are in thermal equilibrium with C, then A and B are in thermal equilibrium with each other.
• First law of thermodynamics: ΔU = Q + W, where ΔU is the change in internal energy of a system, Q is the amount of heat added, and W is the work done ON the system. Q > 0 if heat is added, and Q < 0 if heat is removed.
• Another version of the first law: ΔU = Q – W, where W is the work done BY the system.
• If a process undergone by a system is represented on a P-V diagram, then the work by the system in going from the state represented by point A to the state represented by point B is the area under the curve connecting A to B.